获取CGPoints的边缘/外部坐标

Question

我有一个功能，用户可以绘制/着色图像的特定区域，然后将绘制区域作为裁剪结果。

目前我将绘制坐标存储在一个数组中，在该过程的最后，我使用 UIBezierPath 和 CGContextClipToMask 来裁剪图像。问题是我只需要存储在数组中的绘制坐标的外部坐标。有没有办法过滤CGPoints只能得到外部坐标？

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    // add the first coordinate
    [points addObject:[NSValue valueWithCGPoint:lastPoint]];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

   // add more coordinates as finger moves
   [points addObject:[NSValue valueWithCGPoint:currentPoint]];

}

- (void) crop {


    CGRect rect = CGRectZero;
    rect.size = self.mainImage.image.size;

    UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0);

     {

        [[UIColor blackColor] setFill];
        UIRectFill(rect);
        [[UIColor whiteColor] setFill];

        UIBezierPath * beziPath = [UIBezierPath bezierPath];

        NSValue * firstValue = [points objectAtIndex:0];
        CGPoint firstPoint = firstValue.CGPointValue;
       [beziPath moveToPoint:[ARCroppingViewController
                       convertCGPoint:firstPoint fromRect1:self.mainImage.frame.size
                       toRect2:self.mainImage.image.size]];

        for (uint i = 1; i < points.count; i++) {


           NSValue * value = [points objectAtIndex:i];
           CGPoint point = value.CGPointValue;
           NSLog(@"point: %@", NSStringFromCGPoint(point));
           [beziPath addLineToPoint:[ARCroppingViewController
                            convertCGPoint:point fromRect1:self.mainImage.frame.size
                            toRect2:self.mainImage.image.size]];

           }

     [beziPath closePath];
     [beziPath fill];


      }


     UIImage *mask = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();

     UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0);
    {

      CGContextClipToMask(UIGraphicsGetCurrentContext(), rect, mask.CGImage);
      [self.mainImage.image drawAtPoint:CGPointZero];

    }

     UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();
     NSLog(@"mask image: %@", NSStringFromCGSize(maskedImage.size));
     self.mainImage.image = maskedImage;

}

Answer 1

为了获得优势，我会在保存阶段保存极值（向数组添加点）。因此保持最高和最低的x和y值。认为它比过滤数组更容易：）

修改的

int xMin, xMax, yMin, yMax;
-(void)resetValues
{
    xMax = yMax = 0;

    xMin = yMin = self.mainImage.image.size.width;
}

- (void)checkForExtremes:(CGPoint)point
{
    // Have my IDE not here for checking the MIN() and MAX(), so using this way :P
    lastPoint.x > xMax ? xMax = lastPoint.x : nil;
    lastPoint.x < xMin ? xMin = lastPoint.x : nil;
    lastPoint.y > yMax ? yMax = lastPoint.y : nil;
    lastPoint.y < yMin ? yMin = lastPoint.y : nil;
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    // add the first coordinate
    [points addObject:[NSValue valueWithCGPoint:lastPoint]];

    [self checkForExtremes:lastPoint];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

   // add more coordinates as finger moves
   [points addObject:[NSValue valueWithCGPoint:currentPoint]];
   [self checkForExtremes:currentPoint];
}

然后，结果是

Answer 2

只需循环遍历点（就像现在一样）但检查每个点并存储x和y值的最大值和最小值。然后在循环结束时，您可以在（现在正方形）选定区域的角落处获得4个点。

CGFloat minX, maxX, minY, maxY;

for (... {
    minX = MIN(minX, point.x);
    maxX = ...
}

CGPoint topLeft = CGPointMake(minX, minY);
CGPoint topRight = ...

您还可以在用户跟踪形状时执行这些计算（您也可以修改贝塞尔曲线路径）。